Field of the Invention
The present invention relates to an addition-curable silicone composition and an optical device. In particular, the present invention relates to an addition-curable silicone composition that provides a cured product having good rubber properties and strength properties, low refractive index, and excellent reliability of a product which is reduced in tack after curing, and an optical device that is encapsulated with a cured product of the composition.
Description of the Related Art
An addition-curable silicone composition includes an organopolysiloxane containing an aliphatic unsaturated group such as an alkenyl group and an organopolysiloxane containing a silicon atom-bonded hydrogen atom (SiH group) (organohydrogen polysiloxane), and is cured by a hydrosilylation reaction to give a cured product. Since such a cured product has excellent heat resistance, cold resistance, and electrical insulation and is transparent, the cured product is used for an encapsulant for various optical applications.
An addition-curable silicone composition used for optical applications and an encapsulant for optical devices formed from the composition require high transparency. In order to achieve high transparency, an organopolysiloxane having a dimethylsiloxane-diphenylsiloxane copolymer or polymethylphenylsiloxane as a main backbone is usually used as a substance having high refractive index.
However, the above-mentioned organopolysiloxane that provides a cured product having a refractive index of 1.54 or more is hard to be synthesized. A cured product of a branched organopolysiloxane in which a phenyl group is introduced may have a refractive index of about 1.53 to about 1.54, but is a hard resin and is not elastic. Further, a composition including a branched organopolysiloxane in combination with a linear organopolysiloxane has been proposed (Patent Documents 1 to 7), but the composition does not sufficiently satisfy transparency, refractive index, elasticity, and the like.
Patent Document 8 proposes an addition-curable silicone composition that provides a cured product having high transparency, high refractive index, and good strength properties, and an encapsulant for an optical device formed from the composition. However, the composition does not sufficiently satisfy the optical device performance to be provided, and in particular, the transmittance of light with a wavelength of 400 nm at 25° C. is poor.